Pluchea carolinensis
(sourbush)

Pictures

Picture	Title	Caption	Copyright
Title Habit Caption Pluchea carolinensis (sourbush); habit. Kanaha Beach, Maui. August 28, 2001 Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Habit	Pluchea carolinensis (sourbush); habit. Kanaha Beach, Maui. August 28, 2001	©Forest Starr & Kim Starr - CC BY 4.0
Title Flowering habit Caption Pluchea carolinensis (sourbush); flowering habit. Kahoolawe. February 08, 2008 Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Flowering habit	Pluchea carolinensis (sourbush); flowering habit. Kahoolawe. February 08, 2008	©Forest Starr & Kim Starr - CC BY 4.0
Title Close-up of flowers Caption Pluchea carolinensis (sourbush); close-up of flowers. Hana Hwy, Maui. February 09, 2004 Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Close-up of flowers	Pluchea carolinensis (sourbush); close-up of flowers. Hana Hwy, Maui. February 09, 2004	©Forest Starr & Kim Starr - CC BY 4.0
Title Seeds and seedheads Caption Pluchea carolinensis (sourbush); seeds. East of north-south runway, Sand Island, Midway Atoll. June 09, 2008. Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Seeds and seedheads	Pluchea carolinensis (sourbush); seeds. East of north-south runway, Sand Island, Midway Atoll. June 09, 2008.	©Forest Starr & Kim Starr - CC BY 4.0
Title Habit Caption Pluchea carolinensis (sourbush); small plant habit, showing leaves. John Prince Park, Lake Worth, Florida.,USA. September 25, 2009 Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Habit	Pluchea carolinensis (sourbush); small plant habit, showing leaves. John Prince Park, Lake Worth, Florida.,USA. September 25, 2009	©Forest Starr & Kim Starr - CC BY 4.0
Title Seedlings Caption Pluchea carolinensis (sourbush); seedlings. Sand Island, Midway Atoll. May 14, 1999 Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Seedlings	Pluchea carolinensis (sourbush); seedlings. Sand Island, Midway Atoll. May 14, 1999	©Forest Starr & Kim Starr - CC BY 4.0
Title Control and removal Caption Pluchea carolinensis (sourbush); removal with EEWF crew. Kanaha Beach, Maui. January 22, 2002 Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Control and removal	Pluchea carolinensis (sourbush); removal with EEWF crew. Kanaha Beach, Maui. January 22, 2002	©Forest Starr & Kim Starr - CC BY 4.0

Identity

Preferred Scientific Name

• Pluchea carolinensis (Jacq.) G. Don

Preferred Common Name

• sourbush

Other Scientific Names

• Conyza carolinensis Jacq.
• Pluchea odorata auct. non (L.) Cass.
• Pluchea symphytifolia auct. non Gillis

International Common Names

• English: cattletongue; coughbush; cure-for-all; curry plant; shrubby fleabane; stinking fleabane; sweet scent; wild tobacco
• Spanish: tabat-diable

Local Common Names

• Kiribati: te kaikare; te karei

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Asterales
•                         Family: Asteraceae
•                             Genus: Pluchea
•                                 Species: Pluchea carolinensis

Notes on Taxonomy and Nomenclature

Pluchea, named after French naturalist Noel A. Pluche (1688-1761), is a pantropical genus of aromatic shrubs or herbs in the family Asteraceae (Wagner et al., 1999). The genus, with between forty to eighty species (Eldenäs et al., 1999), is composed of several entities which have been given generic status and is regarded as heterogeneous and not monophyletic (Kadereit and Jeffrey, 2010).

There has been some confusion surrounding the nomenclature of P. carolinensis, including misapplication of the binomial P. symphytifolia (Gillis, 1977; Khan and Jarvis, 1989). This name is actually a synonym for Neurolaena lobate, another medicinal plant with an overlapping range that is used for many of the same purposes as P. carolinensis (Morton, 1981; Hodges and Bennett, 2006). The name P. odorata has also been misapplied to P. carolinensis in Texas, California and Hawaii (Wagner et al., 1999; Hodges and Bennett, 2006).

The species name carolinensis means “of Carolina” as it was erroneously believed to have originated from this region when the species was first described in 1789 (Hammer, 2004). The common name “sourbush” and others associated with smell refer to the aromatic foliage and the name “cure-for-all” derives from the many medicinal and herbal uses associated with the plant (Francis, 2004).

In the Hawaiian Islands, P. carolinensis overlaps in range and distribution with P. indica, an invasive shrub native to southern Asia. Where the two species co-occur, they are able to form spontaneous hybrids classified as P. x fosbergii (Wagner et al., 1999).

Description

P. carolinensis is an erect, many branched, aromatic, tap rooted shrub or subshrub, 10-40 dm tall. Stems are glandular tomentose or matted villous with viscid, vitreous hairs, sometimes merely glandular.

Leaves are petiolate, dull grayish green on upper surface and pale on the lower surface. Leaf shape is elliptic to narrowly ovate or oblong-obovate, 5-20 cm long, 2-8 cm wide. The lower leaf surface is usually densely tomentose. Margins are entire or with small, callous teeth. Petioles are 1-2.5 cm long.

Flower heads are in large, flat topped inflorescences. The involucre is hemispherical, 4.5-6 mm high. The inner bracts are pubescent on the outer face and margins are ciliate. Disk corollas are whitish to pinkish lavender. The pappus is dull brownish white, consisting of a single series of 10-12 capillary bristles. Pappi are tardily falling. Achenes are dark brown, ca. 0.8 mm long, scarcely grooved and sparsely appressed whitish pubescent (Wagner et al., 1999; Flora of North America Editorial Committee, 2015).

Plant Type

Distribution

P. carolinensis has a broad native distribution that includes Mexico and Central America, most islands of the Caribbean and northern South America (Missouri Botanical Garden, 2015; USDA-ARS, 2015). There is some disagreement as to its status in Florida. Some sources list it as native (USDA-ARS, 2015), although most state that it has probably been introduced and has naturalized (Flora of North America Editorial Committee, 2015; The Institute for Regional Conservation, 2015). It has also become widely naturalized on several islands of the Pacific, as well as in Taiwan, Diego Garcia in the Indian Ocean (PIER, 2015; USDA-ARS, 2015) and was most recently first collected in the Canary Islands off the northwest coast of Africa (Verloove, 2013).

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

P. carolinensis was first collected on the island of Oahu, Hawaii, in 1931 (Wagner et al., 1999). Although the exact area of origin and reason for introduction are unknown, the specimen label from the first collection describes the site as “on recent coral fill” on Honolulu (Bishop Museum, 2015). This suggests that it could have been a contaminant in construction material and likely arrived inadvertently through transoceanic shipping activities. Numerous collections in the early 1930s document its rapid dispersal across the island of Oahu and in 1933 it was collected near Hilo on Hawaii Island, possibly also as a contaminant on interisland shipping materials (Bishop Museum, 2015). Subsequent collections were made on the islands of Kauai in 1947, Lanai in 1963, Maui in 1970, Molokai in 1972 and Kahoolawe in 1980 (Bishop Museum, 2015).

The advent of World War II and the movement of large amounts of supplies, construction materials and equipment associated with military activities and installations, likely facilitated the spread of P. carolinensis throughout islands of the Pacific, with the Hawaiian Islands as the most likely seed source. This species began to be noted and collected after the end of the war on the island of Guam in 1946, Eniwetok Atoll, Marshall Islands in 1946, Majuro Atoll, Marshall Islands in 1950, Palau in 1950, Kwajalein Atoll, Marshall Islands in 1950, Tinian, Northern Mariana Islands in 1952 and several of the Northwestern Hawaiian Islands administered by the US government (Bishop Museum, 2015). The correlation between the presence of P. carolinensis and military airfields constructed during World War II has been noted as being the most likely cause of its widespread dissemination throughout its introduced Pacific range (Space and Imada, 2004; PIER, 2015).

P. carolinensis was first collected in Taiwan in 1987 and has rapidly expanded its range across the island, although the area of origin is unknown (Peng et al., 1998). It was also first noted and suspected of being accidentally introduced on the island of Gran Canaria, Canary Islands, in 2011 (Verloove, 2013). It has flowered and set seed in subsequent years and is predicted to become established and fully naturalized in the near future (Verloove, 2013).

Introductions

Risk of Introduction

Within its native range, P. carolinensis has a history and tradition of herbal and medicinal uses (Francis, 2004; Hodges and Bennett, 2006). Such practices could result in its introduction into new areas for similar purposes.

The movement of supplies and equipment associated with military activities is suspected of dispersing the seeds of P. carolinensis over long distances throughout the Pacific (Space and Imada, 2004; PIER, 2015). The possibility still exists that similar dispersal may occur from infested sites if proper precautions or mitigation measures are not in place.

Once P. carolinensis has been introduced and established into a new region, it produces numerous, wind dispersed seeds and has the ability to rapidly colonize and thrive in disturbed sites, often associated with human activities. These are factors that increase the likelihood and risk of further natural and inadvertent introduction.

Habitat

P. carolinensis is commonly found in natural and anthropogenic disturbed sites within both its native and introduced ranges. It can be found occurring along roadsides, road cuts and fill, along the borders of hammocks, on construction sites, riverbanks, vacant lots, eroded sites, landslides, burned areas, the margins of hardwood forests and abandoned fields (Francis, 2004; Hammer, 2004; Flora of North America Editorial Committee, 2015). In Cuba, it occurs in sandy and rocky coasts, anthropic savannahs, ruderal zones and human impacted swampy areas (Herrera and Ventosa, 2005). In the Hawaiian Islands, it is most abundant in relatively dry, coastal areas, pastures, forests, roadsides and vacant lots but can also be found up to 900 m in openings of mesic and wet forests (Wagner et al., 1999; Motooka et al., 2003). In Taiwan, it is a ruderal species in disturbed places, barren mudstone slopes or associated with scrubby roadside vegetation from 50 to 200 m (Peng et al., 1998).

Habitat List

Biology and Ecology

Genetics

Chromosome number of 2n = 20 has been reported (Wagner et al., 1999)

Reproductive Biology

P. carolinensis reproduces through the production of prolific numbers of wind dispersed seeds (Francis, 2004; Cate, 2007).

Physiology and Phenology

P. carolinensis is a fast growing perennial shrub, probably capable of reaching reproductive maturity in a suitable habitat during the first year of growth. It is reported to bloom between the months of February to August in Florida and during the spring months in Texas (Long and Lakela, 1976; Smith, 1985; Hammer, 2004; Richardson and King, 2010). Its flowers are regularly visited by honeybees.

Longevity

P. carolinensis is a short lived perennial shrub, growing for two to four years before dying, or dying back and resprouting from the roots (Francis, 2004). Resprouts grow rapidly, at the rate of up to 1.5 m in the first year of regrowth (Francis, 2004). It is moderately tolerant of fire and can regenerate from basal shoots following low intensity fires (Smith, 1985). P. carolinensis will rapidly colonize burned sites along with a number of early successional weedy species (Smith and Tunison, 1992). Seeds are orthodox although longevity of the soil seed bank is unknown (Royal Botanic Gardens Kew, 2015). One study in the Hawaiian Islands collected P. carolinensis seeds in the soil seed bank over a nine month period, despite their absence in the seed rain, suggesting that seeds may be able to persist under natural conditions for an extended duration of time (Bakutis, 2005).

Associations

P. carolinensis is often found with other ruderal species typically present in naturally and anthropogenically disturbed habitats (Francis, 2004). In Cuba, it exploits these habitats along with Pseudoconyza lyrata [Blumea viscosa] and two species of Pterocaulon (Herrera and Ventosa, 2005). In Florida, it is reported to be a common species in disturbed sites, especially in black mangrove (Avicennia germinans) habitats (Hodges and Bennett, 2006). On the windward aspects of Molokai, Maui and Hawaii islands below 350 m elevation, P. carolinensis is a common component of Wikstroemia shrubland (Wagner et al., 1999).

Environmental Requirements

P. carolinensis is native to areas with a tropical to subtropical climate (USDA-ARS, 2015). It is typically found from sea level to below 1000 m elevation in both its native and introduced range (Wagner et al., 1999; Francis, 2004; Flora of North America Editorial Committee, 2015). It occurs on all soil types and is tolerant of both well and poorly drained soils, all soil textures, acidic and basic pH, salt and salt spray and compaction (Francis, 2004). In the Hawaiian Islands, it has a broad ecological amplitude, but is primarily dominant in coastal habitats and in areas susceptible to brackish groundwater intrusion (Wagner et al., 1999). It grows in areas with an average of at least 1000 mm of annual rainfall, but can establish and persist in much drier sites if sufficient ground water is available. For example near streams and other riparian habitats, wetlands and mangrove communities (Francis, 2004; Erickson and Puttock, 2006). Due to its shade intolerance and inability to compete with dense grass or shrub cover, it is an early successional species that is most common and sometimes dominant in open, disturbed habitats (Smith, 1985; Francis; 2004). Francis (2004) speculates that the wind dispersed seeds require bare, wet soil to germinate and establish. 

Climate

Latitude/Altitude Ranges

Air Temperature

Rainfall

Rainfall Regime

Soil Tolerances

Soil drainage

• free
• impeded
• seasonally waterlogged

Soil reaction

• acid
• alkaline
• neutral

Soil texture

• heavy
• light
• medium

Special soil tolerances

• saline
• shallow

Natural enemies

Notes on Natural Enemies

The flower head feeding fly Acinia picturata (Diptera: Tephritidae), was deliberately introduced from Mexico into Hawaii in 1959 to provide biological control of P. carolinensis. Despite becoming well established, A. picturata was found not to have a significant impact on P. carolinensis (Alyokhin et al., 2001). 

The lobate lac scale Paratachardina lobata, is also a common pest of this species. Adults, larvae and eggs of the polyphagous scale can be introduced into new areas on the stems and leaves of P. carolinensis.

Means of Movement and Dispersal

Natural Dispersal

P. carolinensis produces prolific numbers of wind dispersed achenes (Francis, 2004). The bristly pappus primarily aids in wind dispersal, but may also provide temporary buoyancy that could facilitate secondary dispersal by water, especially in the riparian habitats, wetlands and mangrove communities where P. carolinensis commonly grows (Francis, 2004; Erickson and Puttock, 2006).

Vector Transmission

There is no evidence that the achenes of P. carolinensis are dispersed by birds, mammals or other biotic vectors, but it may be possible that the bristly pappus could aid in adherence to fur or mud on animals.

Accidental Introduction

The movement of supplies and equipment associated with military activities is suspected of being responsible for the dispersal of the seeds of P. carolinensis over long distances throughout the Pacific (Space and Imada, 2004; PIER, 2015).

Intentional Introduction

Within its native range, P. carolinensis has a history and tradition of herbal and medicinal uses (Francis, 2004; Hodges and Bennett, 2006). Such practices could result in its introduction into new areas for similar purposes. Despite the medicinal uses, however, there was no evidence found that it is widely grown or sold commercially outside of areas within its native range. 

Pathway Causes

Pathway Vectors

Impact Summary

Economic Impact

Environmental Impact

Impact on Habitats

As an early successional species generally intolerant of shade and competition, P. carolinensis is most likely to occur in disturbed habitats, which are also negatively impacted by several other fast growing weedy plants. In these sites it may be difficult to discriminate the effects of one taxon from another. P.carolinensis, with its ability to rapidly colonize such sites and form dense monocultures, has been implicated in overall habitat degradation and displacement through competition with native species (Smith, 1985; Motooka et al., 2003). After invading burned sites of the Hawaiian Islands, it is however usually outcompeted and replaced by later successional plants (Smith and Tunison, 1992).

P.carolinensis is also considered to be a primary threat to anchialine pools throughout the coastal areas of the Hawaiian Islands (Pratt and Abbott, 1996). In particular, it produces abundant leaf litter that can contribute to increased eutrophication and early pool senescence (Chai et al., 1989).

Impact on Biodiversity

P. carolinensis primarily invades areas of natural and anthropogenic disturbance, along with several other early successional weedy taxa. Therefore, its impacts on biodiversity in these sites may be minimal. Nevertheless, with its ability to form dense monocultures, it can monopolize resources, displace native flora and interfere with native plant succession in invaded sites. As a result, it has been identified as one of the primary weed threats to 12 species or subspecies of proposed or endangered plant taxa in the Hawaiian Islands. These include Abutilon eremitopetalum, Bidens hillebrandiana subsp. hillebrandiana [B. hillebrandiana], B. micrantha subsp. ctenophylla,Cyanea undulata,Cyrtandra munroi, Dubautia pauciflorula,Euphorbia celastroides var. kaenana,Kadua st.johnii, Labordia triflora,Melanthera micrantha subsp. exigua, M. micrantha subsp. micrantha and Pittosporum halophilum (Wood and Kiehn, 2011; US Fish and Wildlife Service 2000; 2003; 2007; 2008; 2012).

Threatened Species

Risk and Impact Factors

• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Gregarious

• Ecosystem change/ habitat alteration
• Modification of successional patterns
• Monoculture formation
• Negatively impacts agriculture
• Reduced native biodiversity
• Threat to/ loss of endangered species
• Threat to/ loss of native species

• Competition - monopolizing resources
• Competition - shading
• Pest and disease transmission
• Hybridization
• Rapid growth

Uses

Economic Value

Within its native range, P. carolinensis is used medicinally and has economic value to the botanicas and herbal shops that sell it in the form of dried powders, cut plants, live plants and oil extracts (Francis, 2004; Hodges and Bennett, 2006).

Environmental Services

P. carolinensis can rapidly colonize and stabilize disturbed areas and may serve as a nurse crop for later successional species within its native range (Francis, 2004). This species is also regularly visited by honeybees and may therefore be an important nectar and pollen source for these and other insects (Cate, 2007). 

Uses List

Environmental

• Erosion control or dune stabilization
• Revegetation

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Detection and Inspection

The movement of supplies and equipment associated with military activities is suspected of having moved the seeds of P. carolinensis over long distances throughout the Pacific (Space and Imada, 2004; PIER, 2015). Despite this, there are no rules or regulations in place specifically targeting the detection, or restricting the introduction of this taxon in interisland or international movement of goods or materials. 

Similarities to Other Species/Conditions

In the Canary Islands, P. carolinensis is superficially similar to the congeneric P. ovalis, but the two species differ in leaf characters. The leaves of P. carolinensis have (sub-) entire margins and are velvety to the touch. In contrast, the leaves of P. ovalis have a serrate margin and are glandular sticky (Verloove, 2013).

In the Hawaiian Islands, P. carolinensis may also superficially resemble the congeneric P. indica or the interspecific hybrid P. x fosbergii but also differs in floral and leaf morphology. The leaves of P. indica are 2.5-5 cm long and have coarsely dentate margins. In contrast, the leaves of P. carolinensis are 5-20 cm long, with a densely tomentose lower surface and have entire margins (or with small, callous teeth). Leaves of P. x fosbergii are green, lustrous and sparsely tomentose to glabrous and intermediate in length between the two parent species (Wagner et al., 1999).

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Physical/Mechanical Control

Smaller plants may be hand pulled or dug up if all of the roots are removed. The ability of P. carolinensis to resprout from roots or basal suckers may necessitate the treatment of larger plants with an appropriate herbicide (Smith, 1985; Francis, 2004).

Biological Control

There are currently no effective biological control agents available for P. carolinensis. A flower head feeding fly, Acinia picturata (Diptera: Tephritidae), was introduced from Mexico into Hawaii in 1959 but has proven ineffective to date (Alyokhin et al., 2001).

Chemical Control

Several herbicides have been evaluated and proven to be effective in controlling P. carolinensis. In particular, it is reported to be susceptible to drizzle applications of triclopyr, foliar applications of 1% glyphosate and applications of 2,4-D and dicamba (Motooka et al., 2002; Motooka et al., 2003).

Ecosystem Restoration

P. carolinensis is a relatively shade intolerant, disturbance adapted species. It may be replaced by later successional species (Smith, 1985; Francis, 2004). By minimizing site disturbance and restoring native plant cover it may provide a measure of biotic resistance and community resilience to reinvasion and establishment of P. carolinensis. 

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Distribution References

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Links to Websites

Contributors

31/05/2015 Original text by:

Charles Chimera, Hawaii-Pacific Weed Risk Assessment, Hawaii, USA

Distribution Maps